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Micrometer sextants.

It's puzzled me for some time, that though Plath of Hamburg had micrometer 
sextants in their catalogue as early as 1906,  British micrometer 
instruments didn't appear until the Heath catalogue in the early 1930s. Or 
at least, that was the earliest date that the National Maritime Museum at 
Greenwich could find.

But I now think there must be a bit of a gap in their collection, and in 
their documentation. Wolfgang Köberer has kindly pointed me to a short piece 
in the Nautical Magazine, vol 121, Jan 1929, pages 89-90, copied here in an 
attachment. It appears that Heath were then marketing their "Rapid-Reader" 
micrometer sextant, which brings forward its introduction in Britain by a 
few years at least; but still many years behind the Germans..

It's interesting to note the criticism of previous micrometer sextants as no 
more than rough-and-ready instruments which have been in existence many 
years. Presumably, this was a disparaging reference to those made by other 
makers than by Heath (most likely, Plath). Even if the drum was then marked 
only to the nearest arc-minute, I would expect it to be possible to 
interpolate to sixths-of-minutes by eye, as long as the readings were 
consistent, and the rack machined precisely enough..

I'm somewhat annoyed that I had left the library before spotting the 
reference to page 10, which looks as though it might hold an advert. from 
Heath on the subject. That will have to wait for my next visit to the 
Bodleian.

George.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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